Method of using ammonium alum in discoloration reduction of foamed vinyl chloride polymers



' er than depolymerize.

' supply such an additive. present invention to supply an improvement intheart of foaming vinyl chloride polymer-containing composi- 'tions witha blowing agent whereby-internal discolora- United States Patent 0lVIETHOD OF USING AMMONIUM ALUM IN DIS- COLORATION REDUCTION OF FOAMEDVINYL CHLORIDE POLYMERS 1 Lawrence Clark and Algirdas C. Poshkus,Lancaster, Pa., assignors to Armstrong Cork Company, Lancaster, Pa., acorporation of Pennsylvania No Drawing. Application January 30,1956

Serial No. 562,020

6 Claims. Cl. 260-25 This invention relates generally to cellularproducts and more particularly to cellular products'containing vinylchloride polymer. Still more particularly, it relates to a method ofreducing the discoloration normally encountered when a vinyl chloridepolymer-containing composition is expanded by means of a blowing agent.

One of the major problems associated with the open mold expansion ofvinyl chloride polymers such as poly- 7 methylene tetramine, and manyother blowing agents in commonuse.

Although' the mechanism of the diseoloration and eellular breakdownprocesses is not. clear, it is postulated that at elevated temperaturesthe thermal energy becomes s'ufiicient to break the primary valencebonds-of high poly-' mers. The polymertends to split off hydrogenhalidefath- Thus, most halogen-containing polymers give off hydrogenhalide when heated.

The removal of an HCl molecule from the polymer chain of a vinylchloride polymer will make the adjacent chlorine an allylic chloridewhich will be more reactive Thus, the initial removal of than a' normalchloride. HCl tends to promote and accelerate stepwise removal of moreHCl along the chain with the consequent formation of a polyene chain.

shown to be highly colored, audit is believed that this Such polyenechains have been in those cases where they have been of aid inminimizing the discoloration.

These deleterious effects appear to be directly related to the internaltemperature of the foam during blowing. Thus, an additive which has theabilityto absorb-heat without otherwise imparting undesirable propertiesto the finished foam would be desirable asa means of directly reducingthe discoloration while preserving the necessary cellular structure.

It is the primary object of the present invention, to It is a furtherobject of the tion is materially'reduced without imparting undesirableproperties to the finished foam.

These objects"have"beeiiachieved in a surprisingly elfective andstraight forward manner. A composition Patented June 24, 2 i I 4 isformed comprising a vinyl chloride polymer and a blowing agent;additional ingredients such as plasticizers, fillers, antioxidants, andother ingredients normally used in the formation of vinyl foams may beadded if desired. To this composition there is added an amountof'ammonium alum effective to reduce discoloration in the foamedproduct. The composition is then heated'toan elevated temperaturesufficient to decompose the blowing agent in accordance with knowntechnics. On cooling, the product will be found to possess little or nointernal discoloration whilefat the same. time possessing excellentcellular characteristics.

Typical examples of the vinyl chloride polymers which may be foamed orsponged in accordance with the method of this invention are polyvinylchloride; vinyl chloride and vinyl acetatecopolymers containing95% vinylchloride and 5% vinyl acetate; vinyl chloride and vinyl acetatecopolymers containing 87% vinyl chloride and 13% vinyl acetate; vinylchloride-vinyl acetate coice polymers containing 91% vinyl chloride and9% vinyl acetate; vinyl resin produced by polymerizing a mixturecontaining 86% vinyl chloride, 13% vinyl acetate, and 1% dicarboxylicacid; and vinyl chloride and other copolymerizable substances. It isalso within the scope of this invention tosponge orfoam blends of suchpolymers with other materials such .as urea-formaldehyde resins,synthetic rubbers, for example butadiene-styrene copolymers,butadiene-acrylonitrile copolymers, and mixtures of synthetic rubbersand resins such as blends of butadiene acrylonitrile copolymers andpolyvinyl chloride. i

Any of a number of plasticizing materials may be used inthe'polymericcomposition. The plasticizers include such materialsasplasticizing alkyd resins, phosphateplasticizers, forexample'tr-iphenyl phosphate, tricresyl'phosphate, andthelike, phthalateplasticizers, forexample dioctyl phthalate, diphenyl phthalate, and thelike. 'Additionally, many'polyesters in synthetic rubbers exert aplasticizingaction on the vinyl chloride polymers, and

these too maybe used if desired. Fillers and stabilizers maybe added,depending on the properties desired in the final foamed product. p

The blowing agent to be used in the present invention As mentionedearlier, such compounds 7 drazide), dinitroso pentamethylene tetramine,and other organic and inorganic agents may be used in accordance withknown methods. 1

To the above-described foamable compositions the present inventioncontemplates the addition of ammonium alum (Al (NH (SO .24H O). Theammonium alum is to be added in an amount of about 0.57% by weight ofthe total foamable composition, and preferably about 0.8%3% by weightof' the composition.

, Smaller amounts than thestated minimum, while beneficial, do notproduce a practical reduction in discoloration. Larger amountsthan thestated maximum, while substantially eliminating discoloration, causechanges in the normal cell structure of the final product which aredeleterious for most uses. The ammonium alum may be added at any pointduring the preparationof the foamable composition which will insurecomplete and intiisadded in the form of a very fine powder.

mate dispersion of the ammonium alum throughout the foamablecomposition. Preferably, the ammonium alum Where a ."plasticizer is tobe used, it is convenient'to grind the ammonium alum and the plasticizerin a ball mill and then add the mix to the remainder of thecomposition.

.In preparing a resin-rubber composition,;a rubber as a nitrile? rubbermaybe bandedpn acold mill :1 eedflwdw qrsereralmi mtesiii Theyiny ichloid r ymer resin, the plasticizer containing the ammonium alum,

' gredients inthe stated amounts, were prepared:

m1 emade-15% vinyl. acetate (Bakelites Bntadiene-acrylonitrile copolymer(25% :acrylo- -A1kydplasticizer .(ParaplexG .60)'.

theblowing agent, and any other materials may beadded either singly oras a mixturp to the mill and milling continued without heating until thebatch is uniformly mixed.

'The'miill temperature may theh the r'aised slo'wly until the=resin andrubber fuse together. The sheets .may be taken from the -mill andT'foamed in that form, or they hardship since the "blowing ofvinylcompositions is fairly uwell' understood by:those skilled inthe art. Asa gen- -as the-inorganic-"hydrates,amines, alkyland earth metaleitratesppicric acid, pentaerythritol tetranitrate, and polylhydriccompounds such as starch and sucrose do not diminishdiscoloration to theextent that ammonium alum does. In fact, many of thecompounds in thoseclasses actually increase discoloration.

i i r Era m le I ,Threecompositions, each containing the following in-Parts VYHI-I) N,N-dicarbethoxy N,N'-dinitr.oso 1,2.-.diamino ethanetoyield a composition containing 038% "1.2%, and 1.4%

by weight. ammonium alum; "respectively, based on the total compositionweight.

I The three, compositions were pelletize d, placed in con- :tainers, andheated in an oven maintained at 300 F.

In each case athermocouplewas imbedded in the center of the foamablecomposition; I

The internal temperature of the composition was measj'used asflfoamingproceeded. A fter 26 minutes in the oven, thecqmpositions {were removedand allowed to "monium alum. Additionally, the-cellular structure of thethree compositions containing the ammonium alum was excellent andpossessed as goodhomogeneity as did "'theqcomposition foamed in the absencefof ammonium alum. i i The thermocouple indicated that the internaltemperature of theffoam was maintained 8-1'5 F; lower in the interior ofthe ammonium alum-containing composi- A similar run containing 2%ammonium alum gave just as good results with anfinternal temperaturedifference over the control of Similar riins containing2% CuSO .5H O,borax, barium citrate, calcium citrate, Ni(NH C1 INi(NH SO a O4-6H2Q Ozo (N 4)2C 3 hy "wquinone monobenzyl ether, respectively, *alljyielded aTo eachmof' the three above-described compositions there was added onthe mill-suificientammonium alum 4 foamed product more intenselydiscolored .throughout the center than the control, Additionally, manyof these compositions showed unusually large cell formation at thecenter.

5 Eicampleill The following ,base composition was made:

Parts Polyvinyl chloride 100 Tricresyl phosphate. 100 2-V-4 cadmiumstabilizer l Dibutyl tin dilaurate 2 N,N-dimethyl, N,N-dinitroseterephthalamide 33 These ingredients were mixed at room temperature to auniform consistency with a Sunbeam mixer. Various amounts of finelydivided ammonium alum were then dispersed thoroughly in 30 part aliquotsof the master batchby-means of a mortar and .pestle The resultinguniform mixtures were poured into small molds, heated -at 320;" for 20minutes, cooled, removed from the press .andimold, and finally expandedin an air oven at 200 F.for .15 minutes. The .cooled cellular productswere examined .visually .for discoloration. Fine uniform texture and"density were essentially the same for all samples; all rsamples'appearedsimilar in every respect except for discoloration .and small gaspockets.

, In theibllowing table the discoloration is assigned a number giving avalue based on visual inspection relative to the control .(almostauniform gray-brown color) to which the arbitrary value of 10 wasassigned. The natural white .color of an undiscolored PVC foam would beone of this comparative scale.

Gas Pock- Discoloratiou (Relative) 10 (Brown) '9 (Pale brown 7 5 (Tan) 2(Pale .brown core).

None 4 reqon We claim:

1. In the. method of forming a cellular product by admixing a vinylchloride polymer with a blowing agent .and' heating the mixture toatemperature in the range of ,abou t.280.3;25 F.,,sutficient todecompose the blowing agent, the improvement which comprisesincorporating in said mixture before heating an amount of ammonium aluminthe range of about t).5%7% by weight based .onthetotalcomposition,-said amount being effective .to reduce discoloration insaid productn 2. The method according to claim lwherein said amount isin therange of about ,0.8%3%.

3. The method according to claim 1 wherein said vinyl chloride polymercomprises polyvinylchloride.

4. "The method according to .-claim 1 wherein said Vinyl chloride.polyme'r comprises a vinyl chloridevinyl acetate. copolymer containingup to about "13% by weight vinyl acetate.

5. In ,the method of forming a cellular product by admixing polyvinylchlorideiwith. a blowing agent, a butadiene-acrylonitrile copolymer, anda plasticizer for said polyvinyl chloride, and heating the mixture to atemperature in ,the. range .of aboutI2809-325 F. suflicient to decomposeS id blowing agent, the improvement which comprises incorporating 'in'saidmixture before heating an amount .of ammonium alum in the. range ofabout 10.5%.-7,% by weight based on the. total composition,

ws i am nntlbe ng eifiective to. reduce .discoloratiql .i

, said p oducta 70 6. jThe methodfiaccording to .claim 5 wherein saidamount l es. in the range .of abou '0- %3%-.

No references J cited.

UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent Noe2,840,534 June 24, 1958 Lawrence Clark et alt It is hereby certifiedthat error appears in the printed specification of the above numberedpatent requiring correction and that the said Letters Patent should readas corrected below;

Column 1, line '72, for "straight forward" read as straightiforwarjdcolumn 3, line 29, after parts" insert are line 45, for

read 0587x102? column 4, line 12, for dinitros'e read we d so lines 34and 35 Example II second table therein, in the heading to the thirdcolumn thereof, for w (No, (Non an? read c111 Signed and sealed. this.26th day of Angler 1958..

(SEAL) I Attest:

KARL Ho AXLINE ROBERT c. WATSON Attesting Oflicer- Commissioner ofPatents

1. IN THE METHOD OF FORMING A CELLULAR PRODUCT BY ADMIXING A VINYLCHLORINE POLYMER WITH A BLOWING AGENT AND HEATING THE MIXTURE TO ATEMPERATURE IN THE RANGE OF ABOUT 280*-325*F. SUFFICIENT TO DECOMPOSETHE BLOWING AGENT, THE IMPROVEMENT WHICH COMPRISES INCORPORATING IN SAIDMIXTURE BEFORE HEATING AN AMOUNT OF AMMONIUM ALUM IN THE RANGE OF ABOUT0.5%-7% BY WEIGHT BASED ON THE TOTAL COMPOSITION, SAID AMOUNT BEINGEFFECTIVE TO REDUCE DISCOLORATION IN SAID PRODUCT.